How to reduce face/poly count for characters while keeping quads?
The "standard" procedure is Retopology: 

using both the "snap onto surfaces" function and/or the shrinkwrap modifier you will build a new mesh projecting vertices onto the charcter you already made. 

In this way you can control the amount of vertices and distribuite them exactly where you need them, following good edgeflows and avoiding triangles and N-gons. 

If the new LoPoly character still misses some important details you can bake a normal map using the "selected to active" function, so that the missing details will be reproduced by the heghts illusion of the normal map texture.